Tag Info

To make a long story short: get_bloginfo( 'template_directory' ) and get_bloginfo( 'template_url' ) simply return get_template_directory_uri().
So, you can shortcut that second call simply by referring directly to the latter template tag.
Refer to source for get_bloginfo().
A few others:
'url' => home_url()
'wpurl' => site_url()
'stylesheet_url' => ...

The two functions output exactly the same thing.
From the Codex entry for get_bloginfo():
'name' - Returns the "Site Title" set in Settings > General. This data is retrieved from the "blogname" record in the wp_options table.
From source:
case 'name':
default:
$output = get_option('blogname');
Neither get_bloginfo() nor bloginfo() do any sort ...

get_stylesheet_directory_uri() returns a value, it doesn’t print anything. So you have to use:
echo get_stylesheet_directory_uri();
get_template_part() is just a wrapper for locate_template(). But the latter has one advantage: It returns the path of the file it has found. Try the following:
$path = locate_template( 'sidebar-front.php', TRUE );
echo ...

While there is no inherent caching in get_bloginfo(), most of information it retrieves is from options and get_option() is cached.
Holding value you need in a variable for using several time is still (marginally in most cases) faster than function call, but I wouldn't bother with explicit dedicated caching.

You cannot use bloginfo() while your are outputting using echo because bloginfo it self also out puts string using echo. Below will work for you, you also have extra double quote which i have removed....
<?php
$attch_id_1 = pn_get_attachment_id_from_url(get_post_meta($post->ID, 'img1', true));
$image_attributes_1 = ...

Open your backend and go to Settings/General. You will see to input fields:
WordPress Address (URL)
Site Address (URL)
The first one correspond to site_url() and the second one to home_url()
So why is there a difference? Because WordPress is able to start from a different site then your blog posts. For example, create a page called 'homepage' and enter ...

What you have:
<link rel="stylesheet" href="<?php echo get_template_directory_uri(); ?>/css/style.css">
should work fine. I've copied and pasted into my header.php and it worked.
But this is not how you should be including css or javascript files. The proper way is to use the wp_enqueue_scripts hook. For instance, say you have javascript ...

The meta description isn't part of the Twenty Fifteen theme.
You mentioned the Yoast plugin in a previous question yesterday, so I guess the meta description comes from there.
According to their API page, there's a filter called wpseo_metadesc that might be what you're looking for.
Here's an untested example:
/**
* Change the Yoast meta description for ...

You can filter template_directory_uri:
<?php
add_filter( 'template_directory_uri', function( $template_dir_uri ){
return str_replace( 'http://example.com', 'https://cdn.example.com', $template_dir_uri );
});
This will change URIs so they point at a CDN subdomain served via HTTPS.

Use get_stylesheet_directory_uri() and get_template_directory_uri() instead. Note that these functions return rather than echo their result. So, for example:
<img src="<?php echo get_template_directory_uri();?>/images/Lynx.gif" alt="castandtubular"/>

You can't check the context while the filter callback is called, because the element is already in the frontend. There are 3 solutions though:
1. jQuery
Search for the element and add html to the places in the name.
2. PHP in element
Get the bloginfo('name'); in the element and change it on that place using PHP.
3. PHP in header
Add HTML to your ...

If your style.css is in /wp-content/themes/themedirectory, and your image is at /wp-content/themes/themedirectory/images/image.jpg, then your css will be this:
background-image: url("images/image.jpg");
You can't use php in a css file, it will not parse unless included via php (instead of with <link>).

The error indicates that your file "floater.php" is being called outside of a WordPress generated page. Add this to the top of the file to be able to use WordPress functions.
EDIT: See Brian Fegter response on using the server path for your include.
if ( !function_exists( 'get_bloginfo' ) )
require( '../../../wp-blog-header.php' ); // check path leads ...

You should include using the server path rather than the URL. This will give you access to WordPress functionality.
include('extras/floater.php');
Update:
The following is to further explain why it's a bad practice to include the file via URL. Here's what's happening:
There is an innate inheritance when you include a file via server path. It has access ...

I’ve written a plugin that replaces the Biographical Info profile field with the WordPress visual editor, TinyMCE, allowing you to editor an author’s biography using rich text using a new function, wp_editor(), that was released with WordPress 3.3.
http://wordpress.org/extend/plugins/visual-biography-editor/
Using this plugin will ensure that the editor ...

First thing I noticed is that your secondary pages link to images using a URL like:
http://www.bowlingventures.com/BVc_13/wp-content/themes/bowlingventures/images/m2u.jpg
whereas your home page uses:
http://www.bowlingventures.com/wp-content/themes/bowlingventures/images/m2u.jpg
Not sure this helps, but perhaps this will help someone else figure out what ...